In AC motor systems, inductance in the motor windings can delay current flow, which results in a phase shift and thus transmission of less net power than when voltage and current of the same RMS values are perfectly matched. Power factor is the fraction of power actually delivered in relation to the power that would be delivered by the same voltage and current without the phase shift. A low power factor does not necessarily imply lost or wasted power, but rather excess current. The energy associated with the excess current is alternately stored in the windings' magnetic field and regenerated back to the line with each AC cycle. Such an exchange is referred to as reactive power. Though reactive power is theoretically not lost, the power distribution system must be sized to accommodate such power.
Capacitors can be used to correct or compensate for a lower power factor. These capacitors, referred to as power factor correction (PFC) capacitors or PFCCs, are used with motor loads to correct for the reactive power caused by the motor winding inductance. However, the PFC capacitors degrade over time, and thus, become less effective in their ability to correct for reactive power over time. A failure to monitor the PFC capacitor condition can lead to linear decline in power factor correction effectiveness and eventually catastrophic failure. For higher powered motor systems, the decrease in overall PFC due to degradation in the capacitors can also lead to a surcharge from the utility.
Some systems and methods for monitoring wear of PFC capacitors include routine direct visual, thermal, or electrical inspection of the capacitors themselves to see if the capacitors are still operating, or monitoring electricity charges from the utility which may reflect a surcharge by the utility due to low power factor. However, these systems and methods may not provide for timely notification, and thus, may not enable timely replacement of the PFC capacitors in the motor system, thereby resulting in inefficient operation of the motor system and additional costs to the user.